Constant-mesh transmissions for motor vehicles have clutches which either lock a gear to the shaft the gear is journaled upon or that allow the gear to rotate relative to the shaft. In automotive type transmissions the clutches generally include a slider sleeve that locks a gear to the shaft it is mounted upon, when slid in one direction and which allows the gear to rotate relative to the shaft it is mounted upon when the slider sleeve is slid in a second direction. These clutches with sliders often include Synchronizers for at least some of the gears. Synchronizers are devices that bring the gear and the shaft it is mounted upon to the same speed before the slider engages teeth on the gear to prevent grinding between teeth on the slider and teeth on the gear. Some transmissions employ synchronizers on the high speed gears only. Other transmissions employ synchronizers on all shiftable gears.
Industrial type machines are known that employ clutches in their constant mesh transmissions that are hydraulically operated. Such transmissions are commonly referred to as power shift transmissions. The hydraulically operated clutches can be engaged and disengaged by hydraulic valves that are either manually controlled or that are controlled by an automatic or semi-automatic control system.
Constant-mesh transmissions with an input shaft, a co-axial output shaft and a counter shaft are used in many vehicle applications. These transmissions have a gear on the input shaft which meshes with a gear on the counter shaft and rotates the counter shaft. A plurality of gears with various pitch diameters are rigidly secured to the counter shaft. Gears are rotatably journaled on the output shaft and are in mesh with the gears on the counter shaft. The gears on the output shaft are selectively locked to the output shaft to transmit torque from the input shaft to the output shaft through the counter shaft. Each gear provides a specific gear ratio. These transmissions generally include a clutch that is selectively operable to lock the input shaft directly to the output shaft so that the input and output shafts run at the same speed. Because the gear on the input shaft is normally rigidly attached to the input shaft, the counter shaft is driven anytime the input shaft is driven and even when a clutch connects the input shaft directly to the output shaft and the counter shaft is not transmitting torque to the output shaft.
The input shaft rotates in the same direction as the power source. The counter shaft rotates in the opposite direction from the input shaft. The output shaft rotates in the same direction as the input shaft when driven by a gear connected to the counter shaft that is in constant mesh with a gear on the output shaft. The output shaft is driven in the opposite direction to move a vehicle in a reverse direction by providing a reverse idler shaft and a reverse idler gear on the reverse idler shaft that is in mesh with a gear on the counter shaft and a gear on the output shaft or can be moved into simultaneous mesh with a gear on the counter shaft and a gear on the output shaft, both of which are locked to the shaft they are mounted on. The transmission is shifted out of reverse by moving the reverse idler gear out of mesh with the gear on the output shaft and the gear on the counter shaft or by allowing one or both of the gears in mesh with the reverse idler gear to rotate relative to the shafts which support them.
A constant mesh transmission with one of the reverse drives described above is disclosed in U.S. Pat. No. 5,105,674 to Rea et al, the disclosure of which is incorporated by reference. The other reverse drive described above with a reverse idler gear that can be moved out of mesh with other gears is disclosed in U.S. Pat. No. 4,337,675 to Holdeman, the disclosure of which is incorporated by reference.
An output shaft can be driven in the same direction as a counter shaft and thus in reverse by mounting a sprocket on the counter shaft, a sprocket on the output shaft and training a chain around both sprockets. The chain reverse drives that have been used in the past have had one sprocket attached rigidly to one shaft and the other sprocket connected to the other shaft by a clutch. The chains used with the sprockets is a multiple link chain that is commonly referred to as a silent chain or a high speed chain. These chains include multiple links that are pivotally connected to each other by pins to form a continuous flexible belt. Chain drives have advantages over the gear drive described above. The advantages include the elimination of the reverse idler shaft and the reverse idler gear described above. Eliminating the reverse idler shaft and the bearings which support the reverse idler shaft reduces the size and weight of a transmission. Transmission size and weight are important factors in transmission design.
The characteristic of a chain drive that is utilized in a chain reverse drive is that they drive the output shaft in the same direction as the counter shaft when trained around sprockets on both the counter shaft and the output shaft. Chain reverse drives have been tried from time to time knowing that they will reverse the direction of rotation of the output shaft. These chain reverse drives have had limited success due to some undesirable characteristics of chain drives. Chain drives generally have a shorter useful life than gears. There is some wear every time the links of a chain pivot around the connecting pins. Pivoting between the links and the connecting pins occurs upon engagement with a sprocket and upon disengagement from a sprocket. In a drive with two sprockets pivoting occurs four times during each complete revolution of the chain. Wear occurs whether the chain is transmitting torque or is running without torque transmission. Wear between the links and the connecting pins of a chain can be reduced by lubrication. During high speed running of a chain, lubricating oils are thrown out by centrifugal force. This occurs even when the chain is running in an oil reservoir. Reverse movement of the typical passenger vehicle is at low speeds and for short distances. Employment of a chain drive at low speeds and for relatively short distances would seem to eliminate durability problems associated with chain drives. The chain reverse drives that have been used in the past have employed chains and sprockets that are driven and run any time the output shaft is driven even when the vehicle is driven in a forward direction and the chain is not transmitting torque to the output shaft. These chain drives frequently run at substantially higher speeds when the vehicle is being propelled in a forward direction by gears than when the vehicle is being propelled in reverse by the chain drive. When a vehicle is driven at the speed limit on a highway for more than a few miles, lubricating oil can be forced out of the pivot connections between the links and connecting pins and the chain can be damaged due to inadequate lubrication. As a result of these problems the useful life of reverse chain drives in passenger vehicles has been unsatisfactory.
The pivoting of the links of chains about their connecting pins requires some power to overcome friction. The power lost to friction in a chain is substantially more than the power lost in gear drives. The heat generated by friction in some chain drives is a serious problem. Heat generation by a chain that runs in an enclosed gear case with lubricant is generally not a problem but power loss is a problem.
Chain drives do not have the gear rattle problems that are common in the gears of constant mesh transmissions. However, chains can flop between the sprockets due to torsional vibrations. This flopping can damage bearings, shafts, sprockets and the chain itself. Flopping can also cause excessive noise. All chain drives create some noise. High speed movement of chain drives often results in excessive noise.